1. Field of the Invention
The invention relates to a motor assembly, and more particularly to a motor assembly for a pneumatic tool.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional motor assembly 1 for a pneumatic tool (not shown) disclosed in U.S. Pat. No. 7,886,840. The conventional motor assembly 1 includes an outer housing 11, a motor cylinder 12, a motor rotor 15, a rotary valve 13, a valve actuator 14, and an inlet bushing 16.
The outer housing 11 includes a rear housing 111 serving as a handle housing, and a front housing 112 that cooperates with the rear housing 111 to define an internal cavity in which the majority of the other elements of the motor assembly 11 are housed. The motor assembly 11 has a main axis (A). The motor cylinder 12, the motor rotor 15, the rotary valve 13, the valve actuator 14, and the inlet bushing 16 are arranged along the main axis (A) within the internal cavity in the outer housing 11.
The motor cylinder 12 includes a motor chamber portion 121 defining a motor chamber 120, and an inlet conduit portion 122 that has an inlet passage 1220 and a forward port 1221 communicating with each other and that is connected with the inlet bushing 16. The inlet passage 1220 communicates with a bushing passage 160 of the inlet bushing 16. The rear housing 111 of the outer housing 11 cooperates with the inlet conduit portion 122 of the motor cylinder 12 and the inlet bushing 16 to define an exhaust passage 114 thereamong. The motor chamber portion 121 of the motor cylinder 12 further defines a forward passage 123 and a reverse passage 124 that communicate with the motor chamber 120.
The motor rotor 15 is supported within the motor chamber 120, and is rotatable about the main axis (A) in response to flow of the motive fluid into the motor chamber 120 from the forward passage 123 or the reverse passage 124. The motor rotor 15 is connected to a work attachment (not shown) of the pneumatic tool such that the work attachment is operable to perform work in response to rotation of the motor rotor 15.
The rotary valve 13 is sleeved rotatably on the inlet conduit portion 122 of the motor cylinder 12, and is rotatable about the main axis (A). The rotary valve 13 has a valve passage 131 that communicates between the forward port 1221 of the inlet conduit portion 122 of the motor cylinder 12 and the forward passage 123 when the rotary valve 13 is located at a forward position and that communicate between a reverse port 1222 in the inlet conduit portion 122 of the motor cylinder 12 and the reverse passage 124 when the rotary valve 13 is located at a reverse position.
The valve actuator 14 has a head in sliding engagement with the front housing 112, and a stem that extends through the front housing 112 to engage the rotary valve 13 such that the head of the valve actuator 14 is slidable to cause movement of the rotary valve 14.
The following are some of the drawbacks of the conventional motor assembly 1:
1. Since the rotary valve 14 is sleeved on the inlet conduit portion 122 of the motor cylinder 12, the rear housing 111 for housing an assembly of the rotary valve 14 and the inlet conduit portion 122 has a relatively large outer diameter.
2. The inlet conduit portion 122 of the motor cylinder 12 is used to connect with the inlet bushing 16 to provide the inlet passage 1220. Thus, the inlet conduit portion 122 of the motor cylinder 12 is required to have a relatively long length along the main axis (A), thereby increasing production material and cost for manufacturing the motor cylinder 12.
3. Due to the presence of the relatively long input conduit portion 122, the conventional motor assembly 1 has a relatively long inlet path that consists of the bushing passage 160, the inlet passage 1220, the forward port 1221, and the valve passage 131, thereby resulting in increased kinetic energy loss due to flow of the motive fluid into the motor chamber 120.